1. Field of the Invention
This invention relates generally to a lip seal and more particularly relates to a composite lip seal coated with an elastomeric material for sealing bore irregularities and split housings.
2. Description of Prior Developments
This invention is primarily intended to improve the lip seal structure disclosed in U.S. Pat. No. 4,243,235 to Repella the specification of which is incorporated herein by reference. Repella discloses a composite polytetrafluoroethylene and elastomeric lip seal bonded directly to a rigid case formed of a metal or plastic material. While this seal structure is generally satisfactory for its intended purpose, several drawbacks hav been associated with the bond interface between the rubber portion of the composite lip seal and the rigid seal case. More particularly, by bonding the rubber portion of the composite lip directly to a rigid surface, an inherent drawback arises wherein the unyielding nature of the rubber-to-metal bond does not well accommodate shock loading of the type commonly experienced in lip seal applications. This can result in premature failure of the bond and shortened seal life.
In order to allow for the surface irregularities frequently present within seal mounting bores, recent seal designs have included elastomeric or rubber coatings over the entire outer surface portions along the outer diameter of the seal case member. Such designs typically necessitate the treatment of the rigid metal or plastic case member with a rust preventative coating, when needed, followed by a subsequent coating of a thermosetting adhesive for effecting a strong bond between the rigid case member and the elastomeric material which covers or coats the case. During the vulcanization of the elastomeric material on the outer portion of the case, the adhesive which entirely coats the case, thermally reacts to form a bond between the elastomeric material and the case. This can present a problem if a composite polytetrafluoroethylene and elastomer sealing element is to be bonded to the case.
That is, in order to complete the assmebly of a composite lip seal to an elastomer-coated case as described above, the thermally set adhesive must be removed from the area on the case to which the composite element is to be bonded. Fresh adhesive must then be applied before the composite element is bonded to the case. This procedure is not only time consuming but is most inconvenient and incurs significant cost.
Accordingly, a need has arisen for an improved method and seal design which avoids the necessity of removing set adhesive from the seal case to provide a clean bond site for a composite lip seal. A further need exists for a composite lip seal which will effectively absorb dynamic shock loads thereby preventing premature seal failure.